Interpretive Summary: Previous research at the Eastern Regional Research Center resulted in the development of fermentation processes for the production of fuel ethanol from the starch in grains of winter barley. The development and scale-up of that fermentation process has now been completed. The next objective was to develop a process for conversion of non-edible components of the winter barley crop such as straw to ethanol and value-added co-products. Conversion of barley straw, which is a cellulosic biomass, to useful chemicals by a biochemical process is difficult because of its resistance to actions of enzymes and microorganisms. To overcome this problem we have developed a pretreatment process designated as “soaking in aqueous ammonia” (SAA) to “soften up” the barley straw so it can be more easily and cheaply converted to biofuels and bioproducts. In this new process, barley straw is soaked in aqueous ammonia solutions, washed to remove residual ammonia, and subject to enzyme hydrolysis to produce sugars that can be fermented by selected microorganisms for production of the desired products. One of the major advantages of the SAA process is minimization of losses of the carbohydrate fractions in the pretreated biomass, thus increasing the availability of fermentable sugars for subsequent bioconversion to useful products. In the research reported here we determined the optimum conditions for pretreatment of barley straw by the SAA process, such as solid:liquid ratio, reaction temperature, and reaction time, to give maximum production of fermentable sugars. The optimum conditions then were used to prepare a batch of pretreated barley straw for use in the development of a bioconversion process for production of ethanol and value-added co-products. This information will be useful to thousands of researchers in universities, companies and government laboratories who are trying to develop economic processes to convert lignocellulosic biomass into biofuels and other bioproducts.

Technical Abstract: Soaking in aqueous ammonia (SAA) pretreatment was investigated to improve enzymatic digestibility and consequently to increase total fermentable sugar production from barley straw. Various effects of pretreatment process parameters, such as reaction temperature, reaction time, solid:liquid ratio, and ammonia concentration, were evaluated and the optimum conditions determined using response surface methodology.
Optimized reaction conditions were 77.6 deg C treatment temperature, 12.1 hours treatment time, 15 wt. % ammonia concentration, and 1:8 solid-to-liquid ratio, which gave a sugar recovery yield of 71.5% (percent of theoretical sugar recovered from the untreated barley straw) with enzyme loading of 15 FPU/g-glucan. In the optimization of the SAA pretreatment process, ammonia concentration, reaction temperature and reaction time were determined to be the most significant factors correlated to subsequent enzyme digestibility. Based on tested conditions exhibiting high sugar recovery yields of >60%, it appeared that ammonia concentration and reaction temperature affected total fermentable sugar production more significantly than reaction time.